Cellular coverage has historically been provided by wireless access networks having base stations, and operating using cellular protocols. Examples of cellular radio access networks include GSM/EDGE RADIO ACCESS NETWORK (GERAN) Universal Terrestrial Radio Access Network (UTRAN), or Evolved Universal Terrestrial Radio Access Network (E-UTRAN).
Wi-Fi is a popular wireless networking technology that uses radio waves to provide wireless high-speed Internet and network connections. The Wi-Fi Alliance, the organization that owns the Wi-Fi (registered trademark) term specifically defines Wi-Fi as any “wireless local area network (WLAN) products that are based on the Institute of Electrical and Electronics Engineers' (IEEE) 802.11 standards.” Wi-Fi is an example of a technology that provides wireless IP connectivity.
GAN stands for Generic Access Network (GAN). It is designed to complement traditional GERAN, UTRAN, or E-UTRAN cellular radio access network coverage by allowing coverage for cellular subscribers to be extended to areas covered by Wi-Fi networks. This is achieved by tunnelling Non Access Stratum (NAS) protocols between the MS (mobile station) and the Core Network over an IP network. These protocols run over top the IP protocol provided by the WLAN network or other radio IP based network. A network node in GAN is referred to as a GANC (GAN controller), and it is used to provide the interworking between the radio IP based network and the traditional GERAN, UTRAN, or E-UTRAN cellular radio access networks.
The MS may have a preferred mode of operation vis-à-vis the use of GAN, or not, that can be configured by the user, or by the operator through various mechanisms. This information is stored in the “GAN Mode Selection Preferences Field”. The modes of operation that the MS may use are GERAN/UTRAN-only, GERAN/UTRAN-preferred, GAN-preferred, and GAN-only.
If the mode selection preference for the MS is GERAN/UTRAN-preferred, then the MS accesses voice or data services in GERAN/UTRAN as long as there is a suitable GERAN cell or a suitable UTRAN cell available. If the MS cannot find a suitable GERAN or UTRAN cell to camp on, and the MS has successfully registered with a GANC, then the MS switches to GAN mode. Being “camped on” a particular cell means that in idle mode, the MS has assessed the surrounding cells that it can see and has chosen a cell which will offer it a suitable radio connection. From the radio propagation point of view it is desirable that the MS camps on a cell with the lowest path loss, however there may be other reasons or criteria by which the MS chooses a particular cell. As the user moves, the camped on cell may become unsuitable. This situation will generate a cell re-selection. (see 3GPP 45.008 Section 6: Idle Mode Tasks). When the MS in GAN mode is able to find a suitable GERAN/UTRAN cell to camp on, or the MS has de-registered or loses connectivity with the GANC over the generic IP access network, the MS returns to GERAN/UTRAN mode.
If the mode selection preference for the MS is GAN-preferred, when the MS has successfully registered with the GAN over the generic IP access network, the MS switches to GAN mode and stays in this mode as long as the GAN is available. When the MS deregisters, or otherwise loses connectivity with the GAN, the MS switches to GERAN/UTRAN mode.
In a given cellular coverage area, multiple different service providers may be available. Each service provider has a respective network referred to as a PLMN (public land mobile network). Similarly, each PLMN may have an associated set of GANCs that control interworking between the PLMN and the GAN, effectively extending the coverage of the service provider. A GANC is typically associated with one PLMN. However a GANC could be associated with multiple PLMNs.
When a MS is attempting PLMN selection in GAN mode, only PLMNs available via GAN may be considered. The MS may be able to connect via several GANCs that are associated with different PLMNs. When the MS moves into GAN, it will ultimately register with a GANC and in doing so has also registered with the associated PLMN for access while in GAN.
A GANC is a physical node. Each GANC can play one or more of three logical roles: provisioning GANC, Default GANC, Serving GANC.
A GAN-capable PLMN (an operator that has GANC nodes associated with its network), stores in memory of MSs the IP address or FQDN (fully qualified domain name) associated with a GAN Controller that can be used to access its network. The GANC that is addressed in memory is referred to as the “provisioning GANC” for that network. Initially, discovery requests are made to the provisioned GANC. This “provisioned” GANC gives access to the HPLMN (home PLMN) and will let the MS know the address of a default GANC (also in the HPLMN). The HPLMN is the PLMN that the mobile device is subscribed to. The default GANC may or may not be the same as the provisioning GANC.
The MS uses the address of the default GANC in order to attempt to register to it. The default GANC is the logical network node for GAN services that is always connected to the HPLMN. The default GANC can accept, reject or redirect registration attempts from the MS. The GANC that ultimately provides access to the MS is called the serving GANC. The default GANC is the logical role of a GANC in the HPLMN, and it may redirect an MS performing the GAN Registration Procedure to a preferred Serving GANC. The Serving GANC and the Default GANC may be the same entity, in which case no redirection is required.
Note that the GANC's physical location is up to the network operator. The MS connects with the GANC by tunnelling over the internet, so the GANC's physical location is irrelevant and meaningless to the MS. A GANC is like the network operator's VPN server that allows mobile stations to connect to the core network (i.e. SGSNs for data and MSCs for voice) from any internet access point.
The process of registering with GAN starts with the transmission of a GA-RC REGISTER REQUEST sent from the MS to the GANC. The MS may or may not be required to select a GANC as part of the registration process. If, during GAN registration, the MS has a choice amongst two or more GANC-PLMN pairs, then GANC selection takes place. The MS may be informed of available GANC-PLMN pairs via a GAN PLMN list. The GAN PLMN list can be sent to the MS as part of the GA-RC REGISTER REDIRECT message, which is sent to the MS from the Default GANC in response to a GA-RC REGISTER REQUEST.
A handover refers to switching the point of connectivity with the network, be it cellular or GAN while communications are active, also referred to as being in dedicated mode (while an active voice call or data session is in progress). A handover into GAN refers to disconnecting from a cellular base station or (e)Node B or equivalent, and connecting to a GANC, while a handover out of GAN refers to disconnecting from a GANC and connecting to a cellular base station or (e)Node B or equivalent. This is to be contrasted with roving into and out of GAN which refers to idle mode transitions.
The signalling between PLMNs to support seamless handovers exists but in practice this is used very rarely, because coordination and synchronization between two networks is considered to be too much overhead. As a result, having to switch PLMNs during an active communication session most often results in a discontinuation of that communication session. This results in a poor user experience.